The word 辛苦 is formed by combining two characters, 辛 and 苦, which independently and historically convey related ideas of hardship and difficulty. 辛 originally implied the pungent, acrid taste of certain foods or the bitterness of toil, while 苦 directly means "bitter", as in flavor or experience. Their combination is not merely additive but conceptually fused, creating a single, more profound unit of meaning that vividly encapsulates the feeling of enduring exhausting labor, hardship, or mental strain, much like the lingering sensation of a pungent and bitter taste together.